1. Technical Field
The present invention relates to fatigue life prediction in rotor materials.
2. Discussion of the Related Art
Fatigue life prediction is an important management task in turbine generators. The casing, valves, and rotor materials are metallurgically degraded under long-term operation in an elevated temperature and high-pressure environment. Cracks due to fracture and creep may initiate and develop in years of service under severe conditions. Reliable life prediction techniques have been desired in the field for maintenance and repair plans to reduce the life-cycle cost.
Despite efforts made over the past decades, several difficulties and challenges remain in the field. Fatigue crack propagation in an elevated temperature and high-pressure environment is a complex and dynamic process, which involves many fields of expertise and empirical judgments. Two major components must be carefully included in fatigue life prediction under the severe environment: (1) time- and temperature-dependent fatigue and creep-fatigue crack growth, and (2) multiple crack interactions and their impact on final fatigue life. Fatigue crack growth is not only driven by the stress intensity factor but also by the J-integral. The interaction among multiple cracks or between cracks and boundaries affects the stress intensity factor and J-integral. The holding time in a typical loading profile for stream or gas turbines also affects fatigue crack growth. It is not easy for ordinary engineers without expertise to successfully perform life prediction.
A system that can manage useful and empirical information required in this process is desired.